A series of heterometallic 3d-4f polyoxometalates as single-molecule magnets

Three sandwich-like [Ln2Fe2(B-α-FeW9O34)2]10− clusters (Ln2Fe4, Ln = Dy (1), Ho (2), and Y (3)) were obtained by reacting Na9[B-α-SbW9O33], Ln2O3, FeCl3·6H2O and KH2PO4. The [B-α-FeW9O34]11− units were formed via the in situ conversion of lacunary polyoxometalates (POM) [B-α-SbW9O33]9− and the Ln3+ ions were generated from the slow dissolution of Ln2O3, both of which play important roles in the synthesis of Ln2Fe4. Ln2Fe4 is the first 3d-4f cluster assembled from d-metal heteroatom-containing POM. The Dy2Fe4 cluster exhibits single-molecule magnet properties with an 80 K energy barrier in an optimal DC field. Cyclic voltammetry tests and controlled-potential coulometry experiments show that the polyoxometalate Fe heteroatom in clusters 1–3 is also electrochemically active.